A battery converts stored chemical energy to electrical energy, which may be conveyed as a voltage potential. As a battery ages its storage capacity and conductance will decrease (i.e., fade) between a Beginning Of Life (BOL) and an End Of Life (EOL). Therefore, observations of battery parameters such as cycle rate (magnitude of current), cumulative cycling time, and storage capacity may be helpful in determining an overall State Of Health (SOH) of a battery over its service life.
In many contemporary battery systems such as lithium-ion (Li-ion), performance limitations at the cell level often relate to the effective rate or kinetics of the charge transfer reaction that occurs at either electrode surface. In terms of general electrochemistry for reversible systems, the electron-accepting charge transfer reaction occurs at the cathode surface during cell discharge, and occurs at the anode surface during cell charge. This overall process becomes more problematic for Li-ion cells having porous heterogeneous electrode materials that are typically covered by passivation films collectively known as the solid electrolyte interphase (SEI). Performance limitations during a cell pulse are then due to sluggish kinetics and are generally manifest by large impedance-driven voltage shifts and reduced power capabilities.
Cell conductance is defined herein as the inverse of cell impedance, where conductance limitations are directly related to a particular cell chemistry (choice of cell materials, their dimensions, and configuration within a cell) and can be more severe under specific operational conditions (for example, low temperature and low State-Of-Charge (SOC)) and at advanced aging of a cell, making it more difficult to accurately model cell conductance for new battery chemistries using classical theories developed several decades ago.
There is a need for systems and methods that provide a modeling capability that more accurately determines, tracks, diagnoses, and predicts conductance characteristics in electrochemical cells and batteries formed therefrom.